Is seems like Janis was the only character who needed to learn something but didn't

Unlike the other girls, she had every right to do what she did. Regina started bullying her for no legit reason, and turned everyone against her.

She's obviously a genuently nice person hense why she befriended Cady and took her under her wing. But Regina deserves everything that happened to her.

Perhaps she should have learned that its wrong to take advantage of people for your own purposes. She wasn't befriending Cady. She was taking advantage of her. Cady had gotten in with the plastics, and was still too innocent and naive to see what was really going on. So Janis used that to get her long awaited revenge at Regina. Even if you're ok with what she did to Regina (btw she was messing with someones physical and mental health), she should be regretful for using Cady.